Browsing by Author "Nuorkivi, Taru"

Bakeries suffer from yearly quality problems in texture of rye bread during the first two to three months after harvest when using newly harvested rye. A cave on the top of the bread below the crust is a typical defect and so are the large holes just under the crust. Previous studies indicate that the endo-xylanase activity decreases over time in the appropriate storage conditions after harvesting. The aim of this Master’s thesis was to understand the impact of the possible difference in the endo-xylanase activity in the newly harvested rye compared to 10 weeks stored rye, on the bread texture properties. The growing conditions were exceptionally dry and hot for the grain samples in this study that might have affected the results. There were six different rye samples from four different locations in Lithuania, Estonia and Finland. The hypothesis in this study was that the decrease in the endo-xylanase activity during the first months after harvest has an impact on the rye baking functionality. The endo-xylanases in a newly harvested rye flour hydrolyze the arabinoxylans in the rye doughs more efficiently compared to the rye which is stored for 10 weeks causing the breakdown of rye bread structure. The xylanase activity, α-amylase activity, fiber content and ash content of the flour samples were analyzed. Furthermore, the texture and specific volume of the bread samples were analyzed. As expected, the xylanase activity decreased over time in the storage according to the swelling number results. There was a decrease in the endo-xylanase activity, but the decrease was not significant. Despite of the decrease in the xylanase activity over time, the sensory evaluation results did not show any significant differences in the texture of the breads baked with the fresh flour samples compared to 10 weeks stored flour samples. The crumb hardness as well as the chewiness of the breads correlated negatively with the swelling curve and endo-xylanase activity results. The breads baked with the 10 weeks stored flour samples were harder compared to the ones baked with fresh flours. There was a positive correlation between the specific volume and the swelling number results as well as between the specific volume and the endo-xylanase activity results. These results confirm that the xylanase activity decreases over time in the stored grains and the decrease in the xylanase activity results in an increase in crumb hardness and decrease in specific volume of the breads.